The invention relates generally to digital photography, and more particularly to digitizing three-dimensional objects from multiple two-dimensional images to produce computer graphics models.
Three-dimensional (3D) digitizers are frequently used to generate computer graphics models. Considerations of resolution, repeatability, accuracy, reliability, speed, and ease of use, as well as overall system cost, are central to the construction of any digitizing system. Often, the design of a digitizing system involves a series of trade-offs between quality and performance.
Traditional 3D dimensional digitizers have focused on geometric quality measures for evaluating system performance. While such measures are objective, they are only indirectly related to an overall goal of a high quality rendition. In most 3D digitizer systems, the rendering quality is largely an indirect result of range accuracy in combination with a small number of photographs used for textures.
Prior art digitizers include contact digitizers, active structured-light range-imaging systems, and passive stereo depth-extraction. For a survey, see Besl, P. J., xe2x80x9cActive Optical Range Imaging Sensors,xe2x80x9d Advances in Machine Vision, Springer-Verlag, pp. 1-63, 1989.
Laser triangulation and time-of-flight point digitizers are other popular active digitizing approaches. Laser ranging systems often require a separate registration step to align separately acquired scanned range images. Because active digitizers emit light onto the object being digitized, it is difficult to capture both texture and shape information simultaneously. This introduces the problem of registering the range images with textures.
In other systems, multiple narrow-band illuminates, e.g., red, green, and blue lasers, are used to acquire a surface color estimate along lines-of-sight. However, this is not useful for capturing objects in realistic illumination environments. Passive digitizers, based on stereo-vision, have the advantage that the same source images can be used to acquire both structure and texture, unless the object has insufficient texture.
View-based rendering systems can also be used, see Nishino, K., Y. Sato, and K. Ikeuchi, xe2x80x9cEigen-Texture Method: Appearance Compression based on 3D Model,xe2x80x9d Proc. of Computer Vision and Pattern Recognition, 1:618-624, 1999, and Pulli, K., M. Cohen, T. Duchamp, H. Hoppe, L. Shapiro, and W. Stuetzle, xe2x80x9cView-based Rendering: Visualizing Real Objects from Scanned Range and Color Data,xe2x80x9d Proceedings of the 8th Eurographics Workshop on Rendering, pp. 23-34, 1997. In these systems, images and geometry are acquired separately with no explicit consistency guarantees.
Laurentini, in xe2x80x9cThe visual hull concept for silhouette-based image understanding,xe2x80x9d IEEE Transactions on Pattern Analysis and Machine Intelligence, 16(2), pp. 150-162, 1994, describes a visual hull as the maximal volume that is consistent with a given set of silhouettes. Although, the visual hull cannot represent surface concavities, it provides a conservative estimate of an object""s structure. The visual hull process can then interactively generates and shades a sampled approximation of the actual visual hull object from a particular viewpoint, see Matusik, W., C. Buehler, R. Raskar, S. Gortler, and L. McMillan, xe2x80x9cImage-Based Visual Hulls,xe2x80x9d Computer Graphics, SIGGRAPH 2000 Proceedings, pp. 369-374, July 2000. The IBVH process is sensitive to changes in ambient lighting conditions, and requires statistical modeling of the background.
Therefore, there is need for a image-based digitizing system that overcomes the problems associated with prior art digitizers.
The invention provides a digitizing system for acquiring and displaying high-quality graphical models derived from a series of captured images. The system according to the invention differs from most three-dimensional digitizers in that it is not primarily a range-imaging system, Instead, it is a texture-based modeling system.
In essence, the system acquires an approximate three-dimensional model based on the image-based visual hull upon which a view-dependent radiance function is mapped. Both the image-based visual hull and the radiance samples are derived from a common image set. The model can be rendered with a real-time point sample rendering engine based on a point sample representation for visualizing the models.
More specifically, a system digitizes a three-dimensional object as a three-dimension model by placing the object on a turntable while taking two sets of corresponding images. The first set of images and the second set of images are obtained while rotating the turntable to a various positions and illuminated the object with the overhead lights and backlights.
There is a one to one correspondence for images in each set for each position of the turntable. Object shape data and texture data are respectively extracted from the first and second set of images. The object shape data is correlated with the object texture data to construct the three-dimensional digital model stored in a memory of a computer system.